New particle formation (NPF) is a major source of global aerosol number concentration yet its contribution to aerosol mass remains unclear. Here we propose a regime framework for NPF mass contributions using aerosol dynamic simulations constrained by atmospheric measurements. We show that new particles can contribute more than 10 μg m^−3 to particle mass under conditions characterized by high initial new particle concentrations, high condensable vapor production rates, and low background condensation sink (CS_bg). Among these influencing factors, the initial CSbg governs NPF mass contribution: NPF contributes significantly to aerosol surface area and mass at an initial CSbg of ~0.001 s^−1 (regime I), while its contribution becomes negligible when CS_bg exceeds 0.01 s^−1 (regime III). Results show that NPF events in urban Beijing occurs mostly in a transition regime (initial CS_bg 0.001–0.01 s^−1, regime II), in which the NPF mass contribution is also modulated by the mass accommodation coefficient of background particles, while events at a Finnish forest site falls in regimes I and II. With a declining CS_bg, NPF mass contribution in urban environments will shift toward regimes I and II, indicating that control of NPF precursors represents an effective strategy for present and future particulate matter pollution.